Switches or interlocks are provided on many work vehicles to prevent the operation of the vehicle entirely, or to prevent the operation of particular subsystems of the vehicle under certain operating conditions.
These switches or interlocks (called “switches” hereinafter) are commonly attached to safety items like seatbelts or safety bars that extend in front of the operator. In these applications, the switches are always in use and cannot be overridden. In other applications, however, it may be desirable or even beneficial to permit the switches to be overridden. This application is directed to a switch configuration that permits the operator to override a switch when certain operating conditions occur.
Skid steer vehicles are very small, very compact, highly maneuverable construction vehicles for use in a wide variety of construction environments. Skid steer vehicles have a small, compact chassis with either two or three wheels supporting left and right sides of the vehicle. They typically have loader arms, which include either a single arm or multiple arms. The arms typically extend adjacent to the operator compartment on either side of the vehicle. The arms pivot up-and-down on the operator's left and right sides within 1 or 2 feet of the operator's shoulders. A bucket is typically fixed to the ends of the arms and extends across the front of the vehicle right in front of the operator, only a foot or two from his feet.
Since the loader arms and the bucket are disposed so closely to the operator, the operator compartment is typically designed to keep his hands, arms, legs, and feet away from the loader arms and the bucket. In the typical arrangement, the skid steer loader has a cage, commonly called a “ROPS”, which surrounds the operator. The cage prevents the operator from reaching out to either the left or the right of the operator compartment toward the loader arms.
The operator typically enters a skid steer loader from the front through a front operator opening. Skid steer loaders have optional front doors that swing forward and away from the front operator opening. These front doors are optional in most skid steer vehicles, since the operator is typically restrained from exiting the front of the vehicle by a seat belt or safety bar.
Since the skid steer vehicle is so compact, however, the front door may interfere with the bucket or loader arms when it is opened. For this reason, a switch is provided to sense the door when the door is closed and in its proper operating position. In the skid steer vehicle illustrated herein, if the loader arms are lifted when the door is open, the loader arms will interfere with the door and damage it.
The door is provided on the skid steer vehicle as a comfort item and is not necessary for the operation of the vehicle. Skid steer operators using skid steer vehicles in extremely cold environments or extremely hot environments insist on operator compartment heating and operator compartment air-conditioning, respectively. This is only possible if the operator compartment is relatively airtight. To provide this airtight capability, clear glass or plastic sheets or windows are attached to the sides of the cage, and a door with a clear glass or plastic window is hingeably attached to the left or right post at the front of the operator compartment.
To enter the skid steer loader, the operator approaches the vehicle, climbs over the bucket (which extends side to side right in front of the operator compartment), grasps the door handle, and pivots the door forward about its hinges. The operator then steps into the operator compartment between two front posts, then closes and latches the door behind him. The operator then sits down in the vehicle, lowers the restraining bar and fastens his seat belt. The operator then starts the vehicle and drives away.
In prior art skid steer vehicles, a door switch was provided that would sense whether the door was open, or closed and latched. If, after entering the vehicle, the operator did not close and latch the door behind him, the switch would not be actuated and would not indicate the door was closed.
This door switch was coupled in series with the electrical coil of the loader lift arm control valve. Until the door was closed and the switch was actuated, it would block all electrical current to the loader lift arm control valve. The loader lift arm control valve would not work. Hence, the loader arms could not be raised or lowered. Until the door was closed, latched, and the switch actuated, the operator could not move the loader arms. This prevented the loader arms and bucket from damaging the door.
This arrangement had a significant limitation: the vehicle door could not be removed. For if the vehicle door were removed, there would be nothing to press against and actuate the switch. Since the switch could not be actuated, the loader arm circuit was disabled and would not permit the loader arms to be raised.
The system was modified to solve this problem by inserting a jumper into the electrical circuit of the switch. Since the door was unable to close the switch because the door was missing, the jumper would provide that capability by electrically connecting the two leads that extended from the vehicle wiring harness to the switch.
The drawback to this arrangement was that the operator had to remove body panels to gain access to the connector connecting the switch to the wiring harness. The operator had to disconnect this connector and replace it with another circuit element that would jumper the two wires together. This process was slow, painful, and not attractive to operators who were unfamiliar with electrical circuits.
What is needed, therefore, is a new system for overriding the door switch when the door is removed. What is also needed is a simple and easy to use process for overriding the door switch. What is also needed is a method of overriding the door switch that does not require the operator to remove body panels. What is also needed is an improved door switch arrangement that is capable of being overridden easily. It is an object of this invention to provide such a system and method.